(i) Field of the Invention
The present invention relates to a rotary compressor which uses carbonic acid gas as a refrigerant and uses polyalkylene glycol or polyalfa olefin as a lubricant or mineral oil as base oil, and more particularly to a structure of a roller and a vane which prevents abnormal abrasion of the roller and vane and is suitable for providing a reliable rotary compressor.
(ii) Description of the Related Art
A compressor used in a refrigerator, an automatic vending machine, a compressor for a showcase or an air conditioner for home/business use has been conventionally utilizing a large amount of dichlorodifluoromethane (R12) or monochlorodifluoromethane (R22) as a refrigerant. Such R12 or R22 is a target of control of CFC""s because it has a problem that it destroys an ozone layer due to ozone crack potential when it is discharged into air and reaches the ozone layer in the upper air above the earth. The destruction of the ozone layer is provoked by a chloric group (C1) in the refrigerant. Thus, a refrigerant containing no chloric group, for example, an HFC-based refrigerant such as R32, R125 or R134a, a hydrocarbon group refrigerant such as propane or butane, or a natural refrigerant such as carbonic acid gas or ammonia is considered as an alternative refrigerant.
FIG. 1 is a view showing a cross-sectional structure of a two-cylinder type rotary compressor to which the present invention is applied. FIG. 2 is a cross-sectional explanatory view showing the relationship between a cylinder, a roller, a vane and others. FIG. 3 is an explanatory view of the vane. The rotary compressor denoted by reference numeral 1 as a whole includes a cylindrical closed container 10, an electric motor 20 and a compressor 30 accommodated in the closed container 10. The electric motor 20 has a stator 22 and a rotor 24 fixed on the inner wall portion of the closed container 10, and a rotary shaft 25 attached at the center of the rotor 24 is rotatably supported by two plates 33 and 34 which close opening portions of cylinders 31 and 32. A crank portion 26 which is eccentrically provided is formed at a part of the rotary shaft 25. The cylinders 31 and 32 are provided between the two plates 33 and 34. The cylinders 31 and 32 (description will be mainly given as to the cylinder 32 hereinafter) have an axis line which is the same as that of a rotary shaft 25. An inlet 23 and an outlet 35 for the refrigerant are provided to the circumferential wall portion of the cylinder 32.
A ring-like roller 38 is provided in the cylinder 32, and the inner peripheral surface 38 B of the roller 38 comes into contact with the outer peripheral surface 26A of the crank portion 26. The outer peripheral surface 38A of the roller 38 comes into contact with the inner peripheral surface 32B of the cylinder 32. A vane 40 is provided to the cylinder 32 so as to be capable of sliding, and an end of the vane 40 comes into contact with the outer peripheral surface 38A of the roller 38. When impetus is given to the vane 40 toward the roller 38 and the compressed refrigerant is led to the back surface of the vane 40, sealing between the end of the vane and the roller 38 is secured. A compression chamber 50 is formed by being surrounded by the vane 40, the roller 38, the cylinder 32 and the plate 34 which closes the cylinder 32 and others. In the rotary compressor 1, for example, polyol ester as a lubricant or polyvinyl ether or the like as base oil is used.
Thus, when the rotary shaft 25 rotates in the counterclockwise direction in FIG. 2, the roller 38 also eccentrically rotates in the cylinder 32, and the coolant gas sucked from the inlet 23 is compressed and discharged from the outlet 35. In the suction-compression-discharge stroke, pressing force Fv is generated at a contact portion between the roller 38 and the vane 40.
Conventionally, a contact surface 40A at the end of the vane 40 with respect to the outer peripheral surface 38A of the roller 38 is formed into a circular shape having a radius of curvature Rv. This radius of curvature Rv has a value which is substantially equal to a width dimension T of the vane 40 and is approximately {fraction (1/10)} to ⅓ with respect to a radius dimension of the roller 38. Further, as a material of the roller 38, one obtained by hardening cast iron or alloy cast iron is mainly used. Also, as a material of the vane 40, stainless steel, tool steel or one obtained by applying surface finishing such as nitriding treatment to such a material is mainly used. In particular, it is general to give the high hardness and toughness to the vane material.
As shown in FIG. 4, the contact state between the roller 38 and the vane 40 can be substituted by a problem of contact between the cylinders having different curvatures. In such a state, when the two elastic substances of the roller 38 and the vane 40 are pressed against each other by the pressing force Fv of the vane 40, they generally have the surface contact instead of the point or line contact. A length of the elastic contact surface d at that moment can be calculated by the expression (7), and the Hertz stress Pmax (kgf/cm2) represented by the following expression (9) is generated at the contact portion (Hertz theory of elastic contact).
Pmax=4/xcfx80xc2x7Fv/L/dxe2x80x83xe2x80x83Expression (9)
(Fv, L and d in the expression (9) are equal to those in the expression (7))
When the surface contact is provided and the Hertz stress is increased in this manner, nitriding treatment for improving the abrasion resistance or surface treatment such as ion coating of CrN is performed to the vane of the rotary compressor which uses the refrigerant including no chlorine in its molecules and employs polyol ether as a lubricant or polyvinyl ether as base oil. However, there are problems that nitriding treatment does not provide the sufficient proof strength, ion coating of CrN may lead to exfoliation of a coating layer and the production cost is increased.
In order to solve the above-described problems in the prior art, it is an object of the present, invention to provide a highly reliable rotary compressor which uses polyalkylene glycol as a lubricant or polyalfa olefin as base oil in a compressor utilizing carbon dioxide which is a natural refrigerant as a refrigerant, and which prevents abnormal abrasion of a roller and a vane.
As a result of attentive study in order to solve the problems, the radius of curvature of the contact surface at the end of the vane which comes into contact with the outer peripheral surface of the roller is changed, although it has a value substantially equal to the width dimension of the vane. In particular, in the rotary compressor using carbon dioxide which is a natural refrigerant as an alternative refrigerant, the radius of curvature is set larger than the width dimension of the vane in a range for assuring the sliding contact surface at a sliding contact portion of the vane and the roller, and polyalkylene glycol as a lubricant or polyalfa olefin or mineral oil as a lubricant is used. Consequently, the Hertz stress can be reduced, and the sliding distance is increased. Furthermore, the stress is dispersed, and a temperature at the sliding contact portion of the vane and the roller can be lowered. Therefore, the present inventor has found that it is possible to provide the highly reliable rotary compressor which has an advantage of sufficiently reducing abrasion of the outer peripheral surface of the roller or the vane by the inexpensive nitriding processing (NV nitriding, sulphonitriding, radial nitriding) without applying the expensive coating treatment to the vane and prevents abnormal abrasion of the roller and the vane, and has attained the present invention.
To achieve this aim, according to the present invention, there is provided a rotary compressor defined in claim 1 including a refrigerating circuit constituted by sequentially connecting a compressor, a condenser, an expander, an evaporator and others by pipes, and using carbonic acid gas as a refrigerant, polyalkylene glycol as a lubricant or polyalfa olefin or mineral oil as a lubricant, the rotary compressor comprising: a cylinder having an inlet and an outlet; a rotary shaft having a crank portion provided on an axial line of the cylinder; a roller which is provided between the crank portion and the cylinder and eccentrically rotates; and a vane which reciprocates in a groove provided to the cylinder and slidingly comes into contact with an outer peripheral surface of the roller, wherein a radius of curvature of the vane at a sliding contact portion with respect to the roller (Rv) (cm) can be represented by the following expression (1).
T less than Rv less than Rrxe2x80x83xe2x80x83Expression (1)
[where T is a thickness (cm) of the vane and Rr is a radius of curvature at the outer periphery of the roller which slides with respect to the vane]
Further, according to the present invention, there is provided a rotary compressor defined in claim 2, wherein, in order to assure a sliding contact surface at a sliding portion of a vane and a roller, T, RV, Rr, E, xcex1, ev have the relationship which can be represented by the following expressions (2) to (4):
T greater than 2xc2x7Rvxc2x7E/(Rv+Rr)xe2x80x83xe2x80x83Expression (2)
sin xcex1=E/(Rv+Rr)xe2x80x83xe2x80x83Expression (3)
ev=Rvxc2x7E/(Rv+Rr)xe2x80x83xe2x80x83Expression (4)
where E is eccentricity (cm) of a rotation center (O1) of a rotary shaft and a center of the roller (O2), xcex1 is an angle formed by a linear line (L1) connecting a center (O3) of a radius of curvature (Rv) of the vane and a roller center (O2) and a linear line (L2) connecting the center (O3) and the rotation center (O1), and ev is a sliding distance between a point at which the linear line (L1) intersects an outer peripheral surface of the roller and a point at which the linear line (L2) intersects with the outer peripheral surface of the roller.
Furthermore, according to the present invention, in addition to claim 1, there is provided a rotary compressor defined in claim 3, wherein, in order to assure a sliding contact surface at a sliding portion of a vane and a roller in consideration of elastic contact during high-load operation, T, Rv, Rr, E and d have the relationship which can be represented by the following expression (8):
T greater than [2xc2x7Rvxc2x7E/(Rv+Rr)]+dxe2x80x83xe2x80x83Expression (8)
[where T, Rv, Rr and E denote the same terms as those in the expressions (1) and (2)]
where L (cm) is a height of the vane is, E1 and E2 (kgf/cm2) are modulus of longitudinal elasticity of the vane and that of the roller, respectively, xcexd1 and xcexd2 are a Poisson""s ratio of the vane and that of the roller, respectively, xcex94P (kgf/cm2) is a design pressure, xcfx81 is an equivalent-radius (cm) calculated by the expression (5) , Fv(kgf) is pressing force of the vane calculated by the expression (6), and d(cm) is a length of an elastic contact surface calculated by the expression (7) using these terms.                               1          ρ                =                              1            Rv                    +                      1            Rr                                              Expression        ⁢                  xe2x80x83                ⁢                  (          5          )                    
[where xcfx81 is an equivalent-radius (cm), Rv is a radius of curvature of the vane (cm), and Rr is a radius of curvature of the outer periphery of the roller which slidingly comes into contact with the vane.]
Fv=Txc2x7Lxc2x7xcex94Pxe2x80x83xe2x80x83Expression (6)
[where Fv is pressing force (kgf) of the vane, T is a thickness (cm) of the vane, L is a height (cm) of the vane, and xcex94P is a design pressure (kgf/cm2) during operation.]                    d        =                  4          ⁢                                                    (                                                                            1                      -                                              v                        1                        2                                                                                    π                      ⁢                                              xe2x80x83                                            ⁢                      E1                                                        +                                                            1                      -                                              v                        2                        2                                                                                    π                      ⁢                                              xe2x80x83                                            ⁢                      E2                                                                      )                            ·              Fv              ·                              ρ                L                                                                        Expression        ⁢                  xe2x80x83                ⁢                  (          7          )                    
[where E1 is a modulus of longitudinal elasticity (kg/cm2) of the vane, E2 is a modulus of longitudinal elasticity (kg/cm2) of the roller, xcexd1 is a Poisson""s ratio of the vane, xcexd2 is a Poisson""s ratio of the roller, L is a height (cm) of the vane, Fv is pressing force (kgf) of the vane calculated by the expression (6), and xcfx81 is an equivalent-radius (cm) calculated by the expression (5).]
Moreover, according to the present invention, in addition to claim 1 or 3, there is provided a rotary compressor defined in claim 4, wherein the vane is formed of an iron-based material having a modulus of longitudinal elasticity 1.96xc3x97105 to 2.45xc3x97105 N/mm2.
Also, according to the present invention, in addition to claim 4, there is provided a rotary compressor defined in claim 5, wherein an outermost surface of the vane is subjected to nitriding treatment by which a compound layer having Fe and N as main components is formed and a diffusion layer having Fe and N as main components is formed under the compound layer.
Additionally, according to the present invention, in addition to claim 4, there is provided a rotary compressor defined in claim 6, wherein the surface of the vane is subjected to nitriding treatment by which only a diffusion layer having Fe and N as main components is formed.
Further, according to the present invention, in addition to claim 4, there is provided a rotary compressor defined in claim 7, wherein an outermost surface of the vane is subjected to nitriding treatment by which a compound layer having Fe and S as main components is formed and a diffusion layer having Fexe2x80x94N as a main component is formed under the compound layer.
Furthermore, according to the present invention, in addition to claim 5, there is provided a rotary compressor defined in claim 8, wherein an outermost surface of the vane is subjected to nitriding treatment by which a compound layer having Fe and N as main components is formed and a diffusion layer having Fe and N as main components is formed under the compound layer, and the compound layer having Fe and N as main components provided on at least side surfaces of the vane is removed.
Moreover, according to the present invention, in addition to claim 7, there is provided a rotary compressor defined in claim 9, an outermost surface of the vane is subjected to nitriding treatment by which a compound layer having Fe and S as main components is formed and a diffusion layer having Fexe2x80x94N as a main component is formed under the compound layer, and the compound layer having Fe and S as main components provided on at least side surfaces of the vane is removed.
In addition, according to the present invention, in addition to claims 1 to 9, there is provided to a rotary compressor defined in claim 10, wherein a material of the roller which slidingly comes into contact with the vane is formed of an iron-based material having a modulus of longitudinal elasticity 9.81xc3x97104 to 1.47xc3x97105 N/mm2.
Additionally, according to the present invention, in addition to claims 1 to 10, there is provided a rotary compressor defined in claim 11, wherein kinetic viscosity of base oil is 30 to 120 mm2/s at 40xc2x0 C.